1. Field of the Invention
The present invention relates to an apparatus and method for performing recordation by irradiating a light beam to a recording medium.
2. Description of the Related Art
It is necessary to control an emission power of a light source (laser diode or the like) to maintain a predetermined constant value during recording operation in order to achieve a satisfactory reproduction performance with a recording and/or reproducing apparatus or an optical disc drive for use with a recordable or rewritable optical disc, such as a DVD-R (Digital Versatile Disc-Recordable), a CD-R (Compact Disc-Recordable), a DVD-RW (DVD-Rewritable), and a CD-RW (CD-Rewritable).
Conventionally, the laser diode is driven by a driving current which is servo-controlled so as to maintain light power at a constant level when reading from an optical disc. When performing recording, the driving current is added with a current necessary to achieve a light power for recording while performing the servo control. FIG. 1 shows power characteristics of the laser diode which is dependent on the temperature of the laser diode. More specifically, the drawing shows a relation of light power (L) versus driving current (Id) in terms of the temperature of the laser diode as a parameter. Light power of the laser diode increases approximately linearly with respect to a driving current when the driving current is larger than an oscillation threshold value (Ith). As the temperature of the laser diode increases, the oscillation threshold value increases while slope efficiency or external differential quantum efficiency (ηd[W/A]) representing a gradient of the characteristics curve decreases.
It is a problem in the above-described conventional driving method of the laser diode that recording light power varies even when the recording is performed intermittently because the external differential quantum efficiency of the laser diode varies as the temperature of the laser diode changes. It is another problem in the conventional driving method that the individual differences among laser diodes cause variations in light power during recording operation, because the temperature dependence of the laser diode characteristics varies from element to element.